In manufacturing multi-gate field effect transistors (FETs) that include a plurality of fin structures (i.e., a FinFET), in order to operate properly, the fin structures must be isolated from the substrate if the FET is built on a bulk substrate. In contrast, a FinFET built on a silicon-on-insulator (SOI) substrate includes a buried oxide layer (BOX) that isolates the fin structures from each other and the substrate.
Various attempts have been made to isolate the fin structures from the substrate for FinFETs built on bulk substrates. For example, a high dose junction implant at the base of each fin may isolate the fin from the bulk substrate. Alternatively, oxide is grown across the bottom of each fin structure. However, the viability of each of these attempts in manufacturing the FinFETs on a bulk substrate is unknown and may be costly.